Today, mobile or radio telecommunication systems usually are outdoor cellular systems and indoor wireless systems, in which each coverage area of an outdoor cellular system or each coverage area of an indoor wireless system has at least one base station or an access point respectively. Each base station and each access point comprises at least one antenna for transmitting and receiving signals to/from user terminals of the systems. It is often desirable to use a common antenna system to transmit and receive signals. The transmitted signals and received signals may lie in different frequency bands. As an example, state of the art cellular frequency bands like AMPS operates at around 850 megahertz (MHz) and the PCS (Personal Communication System) at around 1900 MHz. Other Communication frequency bands include the PCN (Personal Communication Network) at approximately 1800 MHz, the JDC (Japanese Digital Cellular) at approximately 800 MHz and 1500 MHz, the GSM system (Global System for Mobile Communications) at approximately 850 MHz, 900 MHz, 1800 MHz and 1900 MHz, and wide band code division multiplexing (WCDMA) systems at approximately 1850 MHz to 2200 MHz. Among other bands are, the GPS system (Global Positioning System) operating at approximately 1575 MHz, Bluetooth at approximately 2400 MHz, WLAN (Wireless Local Area Network) at approximately 2400 MHz and 5000 MHz and WIMAX (Worldwide Interoperability for Microwave Access) operation in the range at approximately 2000 MHz to. 5800 MHz.
A problem with introducing and using different frequency bands is that antenna systems are getting more complex and also more electronics, more antennas and more cables are required in the antenna systems or close to the antennas. A common approach of minimizing the number of cables, electronics and antennas in antenna systems is to use feeder sharing, e.g. DC power sharing and/or signalling sharing between frequency bands, dual band tower mounted amplifiers and multi-band antennas. However, introducing more electronics, more cables and more antennas often require redirecting signalling paths and DC paths, which may introduce additional radio frequency losses which, as well known in the art, must be kept at a minimum, i.e. attenuated good enough because of the stringent requirements when it comes to the level of unwanted radiation on RF ports. The generated radio frequency losses are especially noticeable when new RF components are introduced in antenna systems for dealing with feeder sharing and signalling sharing.
In addition, advanced multi-band antenna systems are consuming more DC power and also require more complex signalling to effectively control active devices in advanced antenna systems, especially in antenna systems wherein antennas operating in different frequency bands (as described above) are co-located on the same antenna mast. DC power is, in such systems, often split in order to feed the different RF components in the different antenna systems. However, there is a limit on how many times the DC power can be split. If the DC power is split too may times, the available DC power may be to low and the RF components may hence not function properly.
Furthermore, input port/ports in RF components, residing in antenna systems, that do not have DC, must be provided with DC blocking components. Introducing new and different combinations of DC paths and/or signalling paths will therefore require additional tailor-made RF components with DC blocking. Thus, introducing additional or future systems operating in new frequency bands into existing antenna systems will unnecessarily be difficult if not impossible.
A further problem concerning co-located antennas, operating in different frequency bands, is that a correct impedance matching (usually to 50 Ohms) is hard to achieve when the signalling is split to more that one RF component of the antenna system. This is true regardless of the type of signalling i.e. low-frequency signalling or high-frequency signalling. In addition, an incorrect impedance matching makes it difficult to recombine the signalling or to further split the signalling. The possibility of splitting of the signalling is therefore also here limited.
An additional problem with advanced antenna systems operating in different frequency bands concerns the case where, for example, the DC power to an RF component operating at a first frequency band is interrupted. In such a case, it is desirable to switch the DC and signalling control to another RF component operating at a second frequency band, i.e. using the other RF component as a backup RF component. However, switching DC and signalling control to the other RF component is very complicated to achieve since the other RF component most probably includes a DC blocking component and the DC blocking component must therefore be removed in order for the RF component to take over the operation of the first RF component. In some RF components, removing a DC blocking component is not an easy task and the only solution is to completely replace the RF component. If this scenario occurs, the operation of the antenna system must be interrupted until a new RF component having no DC blocking component is installed. In addition, it is possible for the RF component or components to be improperly connected during installation so that the antenna system will not work as desired. Determining the cause of the malfunction or locating an improperly connected device is usually a very difficult task leading to additional delays in “reviving” the antenna systems.
Today, there exist mainly two solutions to deal with the DC and signalling paths in RF components. One common solution is to provide, in advance, a DC blocking capacitor in the RF components. In such components, although the DC blocking capacitor can effectively block the DC as desired, the signalling is still forced to follow a predetermined signal path or signal paths. These types of components are therefore most usually tailor-made in order to fulfil the requirements of the customer. In other words, a supplier of RF components has to manufacture the RF components in different versions and models depending on the requirements of the customers.
Another common solution is to manufacture only one model but using external DC blocking and signalling blocking components. A drawback with this solution relates to additional radio frequency losses introduced when external components are connected to RF components. Furthermore, this solution introduces additional costs of antenna systems; especially as RF connectors and RF components generally already bring substantial costs to antenna systems. Thus introducing additional components will certainly raise costs, which makes this solution unattractive to operators and/or RF component suppliers. In addition, although external DC blocking components which will normally be seen as open circuits for used signalling frequencies may be utilized, there is a risk that the signalling results in a short circuit if the external component is placed at a position where the cable length is close to N·λ/4, where λ is the wavelength and N is an odd integer number i.e. 1, 3, 5, 7 etc.